Chemical Equations
by vacant houses
Summary: One-shot. A romance fic of sorts but not really. Don and April share a kiss and it's everything that Donatello expected. There were times when April O'Neil was forcibly reminded that her five mutant friends are not human. This is one of them. Mentions of Mikey/Angel.


TMNT are not mine.

Written because I'm a biologist and unable to read human/turtle fics without injecting reality and science into the situation.

* * *

There were times when April O'Neil was forcibly reminded that her five mutant friends are not human.

They didn't occur in the many moments of wild adventure or the wonderful mysteries that they so often stumbled upon. No, April was very much a product of modern society, raised on fanciful stories of heroes and monsters with superhuman skills and abilities. That her characters came with green skin and shells was not all that strange, movies, books and television shows have weirder creations. When she and her terrapin friends were stuck in the midst of yet another improbable occurrence, those were the times when the turtles were _most_ human to her.

It was the quiet moments when the realizations came. After April had become such a permanent feature in the turtles' lives that they lowered their guard when she was in the lair, relaxed and comfortable with her presence. Then she saw the little things, the odd habits they had accumulated from surviving down in the sewers mixed with the little exposure of human life they had picked up from watching television.

She could remember the first time she saw Michelangelo casually reached out and grabbed a spider off the floor and ate it. There had been no conscious thought on his part, he had been talking animatedly and discussing the latest Batman movie with her whilst lounging on the couch. He didn't stop, just kept going whilst April's brain had screeched to a horrified halt. She caught herself quickly though, the manners her parents had instilled kicked in and pointed out that staring was rude.

It was a short time later that she came to realize that the turtles wouldn't have always had food, human food for that matter, whilst growing up in the sewers. They would have had to eat anything they could find. If she replaced the image of the spider with a bowl of chips, Michelangelo's actions were identical to that of a human. The juxtaposition provided little comfort with settling her mind though, it just emphasized that gap, the divide between human and not.

Then there was a time when she hadn't seen the turtles for several weeks and decided to pay them a surprise visit. Given how filthy they had been, she'd initially thought there had been a flood and the turtles had been caught in a torrent of mud. However it hadn't rained for days and the water levels had been low in the sewers.

When she had wondered whether there had been a mud fight, the turtles had a brief moment of complete confusion. Clarifying that they were extremely dirty lead to an awkward pause, the sort where one party has just realised they had committed a faux pas and the other realising that the first party had no understanding of why.

It eventually made sense to her, the turtles were accustomed to the dirt of the sewers and their bodies had acclimated to the conditions they were in, developed immunities to the microorganisms that lived down there. Disease and infection were not things they had to worry about and without the restraints of polite society to enforce cleanliness; the turtles simply did not bother except when she was around. Then they were squeaky clean, unnaturally clean for people who lived in the sewers and she couldn't believe that she had never seen it before.

There were so many little instances and April, with her keen scientist eyes and mind, saw most and came to understand them. Casey, she knew, was near oblivious. Gradually, the strangeness of each habit wore away until the next time she saw something new. But there were plenty of distractions, alien spaceships, evil ninja clans, robot scientists and monsters and madness and so many things that did not just belong. And that was when the turtles were so wonderfully familiar, so strong and capable and completely unbelievable and yet so, so human, just like something out a story.

And then there were moments like now.

"You want to do what exactly?" April repeated quietly.

She and Donatello were alone in the lair and she wasn't sure if that was by coincidence or design given Donatello's request. The turtle gazed calmly back at her, there was no humour in his eyes to indicate that this was a joke, just simple, plain curiosity.

Donatello exhaled roughly. A detached part of April's mind noted that he was simply mimicking human behaviour, affecting nervousness to connect better with her.

"I understand," he began softly, "That people normally just don't ask like this and they tend to attach all sorts of emotional baggage to it which make things unnecessarily complicated. But I'm worried about my brothers, well Mikey in particular. Leo and Raph are a bit more…"

He floundered for the words and April knew at that moment that he was just as aware of the differences between them as she was. None of the turtles had ever dared to acknowledge that they _weren't_ human in words before in her presence.

"Responsible?" she supplied incorrectly.

Donatello looked pensive, like he was about to correct her and then thought better of it. He was almost compulsive when it came to logic and truth. "Sort of," he accepted. "The thing is, he watches a lot of television and reads a lot of comic books. He's a bit more hopeful of his chances with humans than the rest of us but he's also a lot more…"

What would happen to their friendship if she made the move first, dared to be the one to recognize the gap? Donatello was speaking to her as a scientist, as this was nothing more than a simple experiment and it was frustrating for him to be this inarticulate because he was worried about alienating her. She owed it to him to respond with equal maturity.

"Heavily influenced by human media?" April finished. She swallowed then continued nervously, "Basically, he behaves a lot like a teenage boy and you are worried that he might get hurt because of that."

She finally returned Donatello's calm gaze and was relieved to discover that he was regarding her as an equal, not as a mutant regarding a human. Nothing had change and yet everything was suddenly different, she could speak freely and openly about _them_ without worry of damaging the amiable relationship they had developed.

"Yes," he said softly, "He thinks a lot like a human boy. And we've been having adventures to places where mutant turtles aren't unusual, where it is possible that we might be able to have companionship. And then we are making friends with more humans, like Angel and Sydney and the homeless street people. According to the television shows that he has been watching, boys his age should have a girlfriend, be interested in physical intimacy."

April watched Donatello carefully. "But not you?"

The turtle smiled wryly. "I think too much, it wouldn't work for me. I don't think it will work for any of us. But knowing it isn't possible isn't the same as having evidence it isn't possible. And when Mikey comes home, upset because things haven't worked out with Angel, I want to be able to explain to him why."

"You really think that will happen?" she asked.

The amusement faded from Donatello's eyes and then a familiar determination filled him, the one she knew well from the many adventures they had shared together. He wanted to protect his brother, could see that there was something he could do and was going to do it.

"Your television makes it easy, two humans place their lips against the others and suddenly they're full of passion and things just advance from there. It won't happen like that, I assure you."

"This," April responded frankly, "Has to be the strangest reason someone wanted to kiss me."

Donatello simply tilted his head and awaited the rest of her response. "If you were human, I would definitely say this wasn't for science. But knowing you, you are genuinely curious and don't mean anything more with this," she paused and studied from him. "You don't see the point, do you? Forming emotional attachments based on physical intimacy?"

"I'm a turtle," Donatello responded bluntly, "Highly mutated and sentient but a turtle nonetheless. We lay our eggs and swim away. We don't kiss. Emotional attachments aren't exactly natural. I can care for you deeply; I do care for you deeply or as well as a mutated animal think it is able. I can understand that you are attractive to other humans but I don't find you sexually appealing."

That cinched it for her, he was being honest and it made scientific sense to her. "Well, thanks," April said with a humoured grin. "You really know how to sweet-talk a girl."

The turtle snorted with amusement. "That wasn't my intention," he said.

And it wasn't. This was nothing but pure scientific curiosity for him and a determination to be able to help Mikey when things came crashing down. Donatello liked his facts, but he liked having evidence to back himself up even more. His brothers depended on him to have a reason for why things were so difficult with their lives.

"Alright," she said. "Let's do this."

His mouth was all wrong, was April's first thought. She had initiated the kiss, knowing that Don had absolutely no experience at all. Then her second thought was, it's a beak, of course it's going to be wrong.

He responded gradually but it wasn't enthusiastically. More curious exploration than fervent passion. The next moments were probably the strangest ones of her life. It was all very mechanical and she couldn't help but recall Donatello had said about thinking too much. This was supposed to be all spontaneous yet she couldn't stop her mental analysis. Eventually, they broke apart and studied each other.

"Nothing," Donatello said with the air of someone that had something long suspected just been confirmed.

"Nothing," April said and was surprised to find it was true. It hadn't invoked _anything_ in her, she wasn't out of breath and didn't feel the slightest bit aroused.

"The hormones are wrong," the turtle said quietly with a shrug, "For you, not me. I don't feel anything because I'm not biologically wired to respond to kissing. You don't feel anything because I don't have the right hormones in my saliva."

She watched him settle back onto his seat comfortably. "Humans won't be able to do anything for you," she said eventually.

Donatello smiled at her but it was a resigned expression. "Of course not," he said. "You never have to think about it but it depends on pheromones and hormones all being correct. The pheromones set off chemical reactions in your body; hormones flood all the right organs and get the blood pumping. The things they don't show on TV because everything just works for you," he tilted his head back and studied the ceiling. "It will never be right for us. No one has the correct signals for us, not even each other."

It seemed so simple in hindsight, the thing that he had obviously figured out beforehand. Objects had mass, gravity was a force, planets rotated around the sun. A living organism was a complex accumulation of chemical pathways and electrical signals and water and carbon and molecules and atoms. They were made from the same basic components but structured differently and no amount of habituation could change that. He was always going to be a turtle and she was always going to be a human. He could learn, could mimic, could behave like a human but he could not make his own biology respond to the wrong chemicals. They were incompatible equations and there was nothing in the universe that could solve them.

"Mikey and Angel…" April began hesitantly.

"Won't last," Don responded. His eyes slid shut, "I wish they did though. I wish it was possible for him. Realistically speaking, trying to make it work would require lots of experimentation on one of us to find the right chemicals. Somehow, I _don't_ see Bishop going through all that trouble to make an aphrodisiac," black humour slid back into his tone.

Well used to the turtles' grim humour, she couldn't help herself, she laughed. "Those would be the most useless super soldiers ever."

"Not unless he was planning to conquer the secret turtle empire," Don bantered back.

"The one that has taken over the world's sewer systems?"

"Yes," he said with great relish, "We are now in an ideal position to take complete control of the world! Soon Mondays will be abolished and cappuccinos will be free!"

And just like that, the strangeness was gone. Don received a call shortly; apparently his brothers had wound up New Jersey somehow thanks to a mysterious girl with an equally mysterious amulet and she had turned out to be an ancient succubus. Fortunately, she was completely unable to work her wiles on his brothers and it had been easy to banish her back to her dimension and all they needed was a lift now.

April let him go by himself; she sat quietly in the lair and stared around at the strange world she had found herself in. The boys weren't human, she'd known that before but now she knew it intimately so. They weren't just funny shaped humans with green skin and a shell, their brains and bodies operated on completely alien frequencies. Their needs and desires were shaped by different genetic instructions but that didn't mean she couldn't be there for them.

They were different.

And different was fine.


End file.
